Search

Currently, numerous robotically controlled steerable needle-based methods have been offered, which can precisely maintain needle tip deflection to monitor premeditated curved paths inside soft tissue. Percutaneous interventions via MIS methods can deliver patients with improved consequences and earlier recovery times than traditional or open surgeries. Precise needle insertions are important for effective procedures, and dynamically piloted needles can intensify system exactness. Current robotic technology can overcome individuals' limitations and upturn the attainment of minimally invasive percutaneous treatment. Needle insertion can also be applied as a “satellite access” area, and parallel calculus can be pushed or broken into the renal pelvis. The main access is applied for the removal of stones, in that way avoiding the formation of various channels and efficiently caring for kidney function. Here, the authors will present the present state-of-the-art insertion needles for MIS, concentrating on the limitations and challenges still open for their application in the medical area.

The working front of a target of ISIS Target Station 2 (TS2) is an assembly of a tungsten core clad with tantalum enclosed within a tantalum water cooling jacket. The aim of the tantalum cladding is to prevent the tungsten coming in contact with the pressurised and fast cooling water. However, a gamma spectral analysis on the cooling water after a target has failed shows the evidence of transmuted products of tungsten such as 175Hf, 172Lu, 182Ta and 187 W in the water. An electron beam weld joint on the tantalum cladding was identified as one of the areas of weakness. The penetration of the weld using the existing method was found to be inadequate and the grains of the weld line were found to be significantly enlarged. A failure of the cladding through the weld joint would cause the target life to be significantly shortened. In order to improve the weld penetration, a study using different settings of the weld parameters such as weld current, oscillation and focus of the beam has been carried out. The study concluded that maximum weld penetration could be achieved using a combination of high weld power, sub surface focus of the electron beam and low material volume around the weld line. A modification in the design of the front of the target has also been undertaken to ensure full penetration at the weld joints. This will prevent water coming in contact with Tungsten through the welding joint. In addition recent EB welding trials with a revised strategy, using multiple passes electron beams at different energies, have been successful in achieving 1350 μm weld penetration. An increase in the longevity of TS2 target and improvements in cooling water quality have been achieved after the modifications.

International audience; The far-infrared (far-IR) spectra of phenol and four ortho-substituted phenol derivatives, including three deuterated analogs, are presented. These spectra, measured using the free electron laser FELIX, are used to compare the performance of Born-Oppenheimer Molecular Dynamics (BOMD) with several commonly used levels of static density functional theory in the far-IR region. The molecules studied here form intramolecular hydrogen bonds of different strengths (except phenol), display diverse degrees of flexibility, and the OH moieties of the molecules provide large amplitude, anharmonic OH torsional modes. Since several of the molecules contain two OH groups, strong anharmonic couplings can also be present. Moreover, the experimental far-IR spectra of phenol and saligenin show overtones and combination bands as proven by the measurements of their deuterated analogs. All these characteristics of the molecules enable us to test the performance of the applied levels of theory on different complicating factors. Briefly summarized, both the strength of the hydrogen bond and molecular rigidity do not significantly influence the agreement between theory and experiment. All applied theoretical methods have difficulties to consistently predict modes that include the anharmonic OH torsional motion, resulting in overestimated intensities and frequencies. Coupling between two OH functional groups provides an additional challenge for theories, as seen for catechol. The various employed theoretical methods are found to complement each other, showing good results for complex harmonic modes in the case of static B3LYP-D3, while improved results are observed for anharmonic modes, including the OH torsional modes and their couplings, in the case of BOMD. Additionally, BOMD calculates the relative intensities better than the other theories. VPT2 reproduces weak anharmonic modes well, but it overestimates shifts and intensities for strong anharmonic modes.

We present a DC slice imaging study of roaming dynamics in the photodissociation of the nitrate radical, NO3, contrasting pure visible excitation with a combination of visible and CO2 laser excitation at 10.6 μm. Images of specific rotational levels of NO are seen to reflect dissociation on the ground and first excited electronic states, as reported in previous work. The branching is obtained for specific rotational levels by comparison to quasiclassical trajectory calculations of the dynamics on these two surfaces. The results for the visible dissociation are found to be very similar to the combination of visible and infrared, raising questions about the nature of the coupling of these surfaces, the extent to which roaming takes place on both, and how the final product branching is determined.

The red-shifts in the acetylenic C-H stretching vibration of C-H center dot center dot center dot X (X = O, N) hydrogen-bonded complexes increase with an increase in the basicity of the Lewis base. Analysis of various components of stabilization energy suggests that the observed red-shifts are correlated with the electrostatic component of the stabilization energy, while the dispersion modulates the stabilization energy.

2-(4'-Pyridyl)benzimidazole (4PBI) can exist in several states of protonation, having three basic nitrogen atoms. The equilibria involving these states, in ground as well as in excited states, are found to be affected significantly by cyclodextrins (CDs). The formation of inclusion complexes of this compound with all three varieties of cydodextrins is observed to be more favorable at pH 9 than at pH 4, due to the predominance of the neutral form of dye at pH 9. The binding affinity of 4PBI to CDs is found to be governed by two factors: (i) the size of the host and (ii) the mode of insertion of 4PBI. We find that, for the host with a smaller cavity (alpha-CD), insertion of the dye with a pyridyl face is favored, whereas, for gamma-CD, the preference is shifted toward the benzimidazole face of the dye. For beta-CD, the binding affinity of the dye is maximum due to perfect cavity matching with the guest. A combination of steric factor and hydrogen bonding interaction is found to be responsible for modulation of the protonation-deprotonation equilibria of the guest molecule in the inclusion complex. Surprisingly, a protonated form is found to be promoted upon inclusion in cydodextrins, under certain conditions. This is an unusual behavior and has been rationalized by prototropism involving the hydroxyl protons of cyclodextrin molecules.

International audience; Saligenin (2-(hydroxymethyl)phenol) exhibits both strong and weak intramolecular electrostatic interactions. The bonds that result from these interactions compete with intermolecular hydrogen bonds once saligenin binds to one or more water molecules. Infrared (IR) ultraviolet (UV) ion-dip spectroscopy was used to study isolated saligenin–(H2O)n clusters (n = 1–3) in the far- and mid-IR regions of the spectrum. Both harmonic and anharmonic (coupled local modes and Born–Oppenheimer molecular dynamics) quantum chemical calculations were applied to assign cluster geometries to the measured spectra, and to assign vibrational modes to all spectral features measured for each cluster. The hydrated clusters with n = 1 and 2 have geometries that are quite similar to benzyl alcohol–water clusters, whereas the larger clusters with n = 3 show structures equivalent to the isolated water pentamer. Systematic shifts in the frequencies of three hydrogen bond (H-bond) deforming modes, namely OH stretching, OH torsion and H-bond stretching, were studied as a function of the hydrogen bond strength represented by either the OH bond length or the H-bond length. The shifts of the frequencies of these three modes correlate linearly to the OH length, despite both intra- and intermolecular H-bonds being included in this analysis. The OH torsion vibration displays the largest frequency shift when H-bonded, followed by the OH stretching vibrations and finally the H-bond stretching frequency. The frequency shifts of these H-bond deforming modes behave non-linearly as a function of the H-bond length, asymptotically approaching the frequency expected for the non H-bonded modes. The nonlinear behavior was quantified using exponential functions.

Our microscopic understanding of intermolecular interactions has increased considerably from the studies on isolated molecular clusters. The intermolecular modes for these clusters are located in far-infrared and terahertz regions and provide a sensitive test of the potential energy surface. Here we report a helium droplet setup (BoHeNDI@FELIX), which is coupled with free electron lasers, FEL-I and FEL-II, at the FELIX laboratory in Nijmegen. These lasers provide tunable radiation in the range of 66–3600 cm−1, covering the intermolecular modes, with average output power of 0.1–0.8 W and spectral bandwidth of 0.2–5% of the central frequency. Mass-selective infrared spectra of propargyl alcohol were recorded in the frequency range of 560–1600 cm−1, which demonstrate the performance of the new setup. The observed vibrational bands could be assigned to the gauche conformer of propargyl alcohol. The high power and micropulse structure of the FELIX radiation allow multiple excitations of the embedded molecules allowing spectral detection with a signal to noise of 10, even in the low-frequency region.

The propargyl radical is considered to be of key importance in the formation of the first aromatic ring in combustion processes. Here we study the bimolecular (self-) reactions of propargyl in a high-temperature pyrolysis flow reactor. The aromatic reaction products are identified by IR/UV ion dip spectroscopy, using the free electron laser FELIX as mid-infrared source. This technique combines mass selectivity with structural sensitivity. We identified several aromatic reaction products based on their infrared spectra, among them benzene, naphthalene, phenanthrene, indene, biphenyl, and surprisingly a number of aromatic compounds with acetylenic (ethynyl) side chains. The observation of benzene confirms that propargyl is involved in the formation of the first aromatic ring. The observation of compounds with acetylenic side chains shows that, in addition to a propargyl- and phenyl-based mechanism, the HACA (hydrogen abstraction C2H2 addition) mechanism of polycyclic aromatic hydrocarbons formation is prese...

The C-H⋅⋅⋅N hydrogen-bonded complexes of several fluorophenyacetylenes with ammonia and methylamine were characterized by a redshift in the acetylenic C-H stretching vibration of the phenylacetylene moiety. These redshifts were linearly correlated with the stabilization energies calculated at the CCSD(T)/CBS//MP2-aug-cc-pVDZ level. Analysis of various components of the interaction energy indicated that the observed redshifts were weakly correlated with the electrostatic component. The weaker linear correlation between the frequency shifts and the electrostatic component between two data sets can perhaps be attributed to the marginal differences in the Stark tuning rate and zero-field shifts. The induction and exchange-repulsion components were linearly correlated. However, the dispersion component depends on the nature of the hydrogen-bond acceptor and shows a quantum jump when the hydrogen-bond acceptor is changed from ammonia to methylamine. The observed linear correlation between the redshifts in the C-H stretching frequencies and the total stabilization energies is due to mutual cancellation of deviations from linearity between various components.

An enhancement in the excited state proton transfer (ESPT) processes of coumarin-102 (C-102) dye was observed upon addition of salicylic acid and hydrochloric acid in sodium dodecyl sulfate (SDS) micellar solution. The phenomenon was observed only in the micellar medium of anionic surfactant SDS and not in case of cationic (CTAB) or neutral (Trition X -100) surfactants. ESPT of C-102 was also observed in aqueous solutions but on addition of very high concentrations of hydrochloric acid. However, on comparing the ratio of the protonated species from the emission spectra in the presence and absence of SDS micelle, a conclusive estimation of the local proton concentration at the Stern layer of SDS micelles could be evaluated.

Process control models can be developed by using both conventional and AI approaches. The conventional approaches include regression models and process kinetic models, and the artificial intelligence (AI) approaches are based on artificial neural nets (ANN), genetic algorithm (GA), and fuzzy rule-based expert systems FRBES. Plant data on hot metal desulfurization, carried out by injecting calcium carbide, is analyzed to test and tune different types and combinations of models and then evaluate their relative performance. Although the control models based on process fundamentals provide a fillip to the new ideas for technological developments and improvements, the combination of conventional and AI approaches may be a better option for process control on the shop floor. It is advisable to first develop and test all models and then decide about the best strategy of using them.

Dynamics of small probe molecules have been routinely used to unravel the intrinsic details of charged ion transport in polymer brushes and polyelectrolyte multilayer (PEM) thin films. However, corresponding morphological properties affected with absorption of moisture have been hardly dealt with despite numerous applications of isotropic thin films in material chemistry and medical purposes. We have explored the overall structural changes associated with plasticization of PVP thin films by probing dynamics of small reporter (rhodamine 6G, Rh6G) molecules using fluorescence correlation spectroscopy (FCS). It was observed that under lesser amounts of absorbed moisture, the rigidity of the film matrix was high enough to inhibit appreciable molecular mobility. Nonetheless, with gradual increase in the moisture level within the film, molecular movement became extremely facile, so much so that it almost attained close to a solution like state. Molecular mobility was found to be dependent on both the method of preparation and the thickness of the thin films. The diffusivities mostly followed anomalous subdiffusive behaviors, reminiscent of dynamics of tracers in crowded cellular environments. The mobility was found to be independent of any electrostatic interaction between probe and polymer thin film. Hence, the tracer dynamics was attributed most likely to the viscoelasticity of the thin film matrix.

In the framework of a simple model of a one-dimensional array of a ferroelectric slab of domains, the polarization with time and space is explained by the Klein-Gordon equation. A perturbation of the K-G equation makes it possible to use this continuum model through a progressive-wave nonlinear Schr\"odinger equation (NLSE). The latter gives rise to a bright soliton that moves with a certain velocity. The bright soliton controls itself so that both bright and dark solitons appear at the same time with discrete energy levels that are estimated from a hypergeometric function, but the dark soliton is not visible as it is part of the complex solution that indicates absorption of energy, i.e., the presence of an energy gap. The pulse width for switching of ferroelectrics can be estimated from the analysis of the NLSE and matches that calculated from this model.

The hydrogen-bonded complexes of phenylacetylene, 4-fluorophenylacetylene, 2-fluorophenylacetylene, and 2,6-difluorophenylacetylene with ammonia are investigated using IR-UV double resonance spectroscopy in combination with high-level ab initio calculations at the CCSD(T)/CBS level of theory. The C-H···N hydrogen-bonded complex, which involves an interaction of ammonia with the acetylenic CH group is the global minimum and is observed in all four cases investigated. In addition, phenylacetylene and 4-fluorophenylacetylene form a quasi-planar cyclic complexes with ammonia incorporating N-H···π and C-H···N hydrogen bonds, wherein the π-electron density of the acetylenic C≡C bond acts as an acceptor to the N-H group of ammonia. A third ammonia complex is observed for 4-fluorophenylacetylene in which ammonia interacts with the fluorine atom once again, leading to the formation of a quasi-planar cyclic complex. The substitution of the fluorine atom on the phenyl ring of phenylacetylene modulates the intermolecular potentials, which are dependent on the position of the substitution.

The hydrogen bonding behavior of trifluoromethylphenols and their water complexes were investigated using IR-UV double resonance spectroscopy. Both ortho- and meta-trifluoromethylphenols exist in the syn conformer, which is the global minimum in both the cases. The IR spectrum in the O-H stretching region reveals the absence of an intramolecular O-H center dot center dot center dot F hydrogen bond in the syn-o-trifluoromethylphenol, which is in contrast to the results reported in the literature. The water complexes of both o-trifluoromethylphenol and m-trifluoromethylphenol are characterized by formation of O-H center dot center dot center dot O hydrogen bonds between the donor phenolic OH group and the acceptor water molecule. In addition, the o-trifluoromethylphenol-(water)(2) complex was also observed.

2,2'-(Pyridyl)benzimidazole is used as a probe to explore proton transfer through nafion membranes. The probe marks the availability of water in native as well as cation-exchanged membrane. Using steady state and time-resolved fluorescence studies, it has been shown that the rotation of the pyridyl and benzimidazole rings with respect to each other, which is ultrafast in higher water contents, is hindered as the water content in the membranes is decreased. In cation-exchanged membranes, it is observed that the formation of the ESPT (excited state proton transfer) state is reduced to a large extent. Thus, it may be inferred that the proton transport is observed to be hindered even in molecular dimensions of one water molecule thereby bolstering the contention that it may not be essential for water channels to break for proton conductivity to decrease.

Two distinct isomers for the binary complex between phenylacetylene and methylamine were observed. The first complex is characterized by the presence of a C-H···N hydrogen bond between the acetylenic C-H group and the N atom of methylamine. In the second complex the N-H group of methylamine interacts with the π electron density of the benzene ring accompanied by a peripheral interaction between the methyl C-H group and the π electron density of the C≡C bond. Stabilization energies and Gibbs free energies at the complete basis set (CBS) limit of the coupled cluster theory with single, double, and perturbative triple excitations [CCSD(T)] suggest that while the C-H···N hydrogen bonded complex is the global minimum, the N-H···π hydrogen bonded complex is a high energy local minimum. The formation of the N-H···π complex could be related to kinetic trapping or higher accessibility. Comparison of the laser induced fluorescence (LIF) excitation and the one-color-resonant two-photon ionization (1C-R2PI) spectra suggests that formation of C-H···N hydrogen bonding leads to fluorescence quenching in phenylacetylene, most probably due to dipolar coupling in the excited state. The binary complex between the phenylacetylene and methylamine shows interesting isomer-dependent fluorescent properties.

State-selected DC sliced images of propenal photodissociation show clear signatures of a novel synchronous concerted three-body dissociation of propenal recently proposed by Lee and co-workers to give C2H2 + H2 + CO [S. H. Lee, C. H. Chin, C. Chaudhuri, ChemPhysChem 12, 753 (2011)]. Unlike any prior example of a concerted 3-body dissociation event, this mechanism involves breaking three distinct bonds and yields 3 distinct molecules. DC sliced images of CO fragments were recorded for a range of rotational levels for both v = 0 and v = 1. The results show formation of two distinct CO product channels having dissimilar translational energy distributions with characteristic rovibrational state distributions. The images for CO (v = 0) show a large contribution of slower CO fragments at lower rotational levels (J = 5–25). This slow component is completely absent from the v = 1 CO images. The images for the higher rotational levels of the v = 0 and v = 1 CO are nearly identical, and this provides a basis for de...

We combine the techniques of infrared multiphoton dissociation (IRMPD) with state selective ion imaging to probe roaming dynamics in the unimolecular dissociation of nitromethane and methyl nitrite. Recent theoretical calculations suggest a "roaming-mediated isomerization" pathway of nitromethane to methyl nitrite prior to decomposition. State-resolved imaging of the NO product coupled with infrared multiphoton dissociation was carried out to examine this unimolecular decomposition near threshold. The IRMPD images for the NO product from nitromethane are consistent with the earlier IRMPD studies that first suggested the importance of an isomerization pathway. A significant Λ-doublet propensity is seen in nitromethane IRMPD but not methyl nitrite. The experimental observations are augmented by quasiclassical trajectory calculations for nitromethane and methyl nitrite near threshold for each dissociation pathway. The observation of distinct methoxy vibrational excitation for trajectories from nitromethane and methyl nitrite dissociation at the same total energy show that the nitromethane dissociation bears a nonstatistical signature of the roaming isomerization pathway, and this is possibly responsible for the nitromethane Λ-doublet propensity as well.